Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for purifying contaminated
coumarin or alkylated coumarin of the general formula
~1
3 ~ ~ R6
R4 R5
wherein each of the substituents R1 to R6 may be hydrogen or a C1-C5 alkyl
group and the total number of carbon atoms of the substituents is not
more than 10.
The preparation of such compounds is described and claimed in
British Patent No. 1,368,941 and Canadian patent application
179.601 Such compounds are of particular importance in the
fragrance industry, and thus have to be very pure. The main standard of
purity generally required is that the colour of the coumarin should be
less than 100, preferably less than 70 Hazen. Common impurities in
coumarin include 3,4-dihydrocoumarin, ethyl phenol, dihydrocinnamic acid,
and e~ter of ethyl phenol and dihydrocinnamic acid. Several methods of
purifying coumarin are known e.g., distillation and recrystallization
16 (see for example Kirk-Ottmer, Encyclopedia of Chemical Technology, 2nd
edition, volume 6). Such methods however yield a coumarin that is not
sufficiently pure for use in the fragrance industry, and for instance the
colour of the coumarin thus purified is between 125 and 250 Hazen.
According to another known method coumarin can be obtained in a purified state
by successively separating the resinous components from the crude coumarin,
dissolving the remaining coumarin in concentrated sulphuric acid, passing air
through the resulting solution at high temperature, precipitating the coumarin
by treating the solution with water, washing and neutralizing the
precipitate and distilling it at reduced pressure. This process is complicated,
and provides a product having a colour of about 200 Hazen, and furthermore
a considerable part of the starting material gets lost.
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In another process describcd in Berichte, Volume 70, 19~7, p. 237,
coumarin is recovered from a roaction mixture obtained by dehydrogenation
of dihydrocoumarin, the reaction mixture is distilled, and the distil]ate
is dissolved in aqueous potassium hydroxide. The solution thus obtained
is treated with an acid and subjected to an extraction with ether. This
laborious process yields a coumarin also that is not sufficiently pure in
practice, and mor~over the dissolving of the mixture in potassium hydroxide
requires a very large amount of potassium hydroxide, viz. about 2.5 mole
potassium hydroxide per 100 grams of reaction mixture.
The present invention provides a process for purifying a
contaminated coumarin or alkylated coumarin of general formula
Rl .
. R2 ~ ~ . ::
R3 ~ R6
R4 R5
wherein each of the substituents R1 to R6 is hydrogen or a C1-C5 alkyl group
and the total number of carbon atoms of the substituents is not more than 10,
comprising treating the contaminated coumarin with an aqueous solution of a -
15 basic compound at a temperature between 20 and 150 C, separating the
aqueous layer thus formed from the layer containing the coumarin, and
' wRshing the latter layer with water at a temperature between 20 and 150 CC~
! and recovering purified coumarin compound from the resulting washed layer.
~ The aqueous basic solution used may be for instance an aqueous solution
i 20 o~ an alkali metal or alkaline-earth metal hydroxide, e.g., NaOH, KOH, LiOH,
Mg(OH)2, Ca(OH)2, and Ba(OH)2. Other solutions which may be used according
to the invention are solutions of sodium or potassium carbonate, sodium or
I potassium acetate, and sodium or potassium benzoate. The amount of basic
¦ compound in the said solution is preferably between 0.001 and 1 mole
1 25 equivalent of basic compound per 100 grams of contaminated coumarin. The
optimum amount is determined in part by the amount and the nature of the
impurities. In most instances it is sufficient to use a solution containing
between 0.005 to 0.1 mole equivalent of basic compound per 100 grams of
contaminated coumarin.
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The conc~ntratic)n of the so]ution may also be within widc limits,
e.g. containing betwecn 0 1 and 10 % by wcight of basic compound. The temperature
at which the treatment of the contaminated coumarin and the washing with water
is effected is preferably of a temperature of from 70 to 100 C. The pressure
is not critical and the process may be effected at atmospheric pressure.
The purified coumarin compound may be recovered from the layer that
has been washed with water in various ways, preferably by distillation.
Coumarins obtained in the process according to the invention are very pure and
can be used as such in the fragrance industry, the colour of the product
j 10 being below 70 Hazen. If it is desired to have extremely pure coumarin, this
may be obtained by recrystallizing the coumarin product recovered by distillation,
e,g. from ethanol.
The following examples of the invention are provided,
,
b Exam~le I
186 grams of impure coumarin and 186 grams of an aqueous sodium
hydroxide solution (0.75 % by weight of NaOH) were introduced into a 500-ml
¦ flask provided with a stirrer and a reflux condenser.
¦ The impure coumarin contained 2 % by weight of 3.4-dihydrocoumarin,
0.2 % by weight of ethyl phenol, 0.3 % by weight of dihydrocinnamic acid and -
ao 0,5 % by weight oi high-boiling impurities mainly the ester of ethyl phenol
` and dihydrocinnamic acid. -
The mixture in the ilask was heated with stirring at 100 C for
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1 hour under reflux. Subsequently the layer containing coumarin was separated
~rom the aqueous layer and the organic layer was washed twice with a total of
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25 180 ml of water. 170 grams o~ coumarin were recovered from the washed product:~ ''~:, , ` . : -
by di6tillation.
The purified coumarin product thus obtained Qontained
. more than 99,9 % of coumarin, together wlth 0.01 % by weight of ethyl phenol,
0.03 % by weight of dihydrocinnamic acid, and 0.03 % by weight of high-boiling
- 30 impurities.
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The colour o:E the product was 65 llazen.
70 grams of the coumarin product were rccrystallized from 250 m] of
50 % cthanol. The coumarin was then filtered and washed twice with a total
of 50 ml of 20 % ethanol. The product was dried and yielded 62 grams of highly
purifiod coumarin of more than 99.95 % purity, together with less than
0.01 % by weight of dihydrocinnamic acid and 0.01 % by weight of high-boiling
impurities.
The colour of the product was 60 Hazen.
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Example II
40 grams of impurc coumarin and 40 grams of a solution of sodium
carbonate in water (0.9 % by weight of Na2C03) were introduced into a 100-ml
flask provided with a stirrer and a reflux condenser.
' The impure coumarin contained 97 % by weight of coumarin, together
with 2 % by weight of 3,4-dihydrocoumarin,0.2 % by weight of ethyl phenol,
0.3 % by weight of dihydrocinnamic acid and 0.5 % by weight of high-boiling
impurities. The mixture in the flask was heated with stirring at 100 C for
1 hour under reflux. Subsequently the layer containing coumarin was separated
irom the layer containing the basic compound and washed twice with a total
I of 40 ml of water. The organic layer was distilled and 36 grams of purified
1, 20 coumarin were obtained of more than 99.9 % by weight of coumarin, together
with 0.01 % by weight of ethyl phenol, less than 0.01 % by weight of
dihydrooinnamic acid and 0,02 % by weight of high-boiling impurities.
¦ The colour of the product was 68 Hazen.
Comparative Experiment
100 grams of impure coumarin having the same composition as the
impure coumarin used in Example I and 100 grams of sulphuric acid (80 % by
¦ weight of H2S04) were introduced into a 250-ml flask provided with a stirrer,
a reflux cooler and a gas-inlet tube. The mixture in the flask was heated at
110 C for 2 hours with stirring and 135 litres/hour of air passed through
the contents,
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The reaction mixture was then poured into 200 ml of water whoreby
a precipitate of coumarin was formod. The precipitate was filtered off,
washed with water and distilled at reduced pressure.
The coulnarin product obtained containcd 99.5 % by weight of coumarin
together with 0.1 % by weight of ethyl phenol, 0.2 % by weight of 3.4-dihydro-
coumarin, 0,02 % by weight of dihydrocinnamic acid and 0.18 % by weight of
high-boiling impurities.
The colour of ~he product was 20 ~ hazen.
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